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28. Development of a Kinetic Model for the Redox Reactions of Co 2.4 Ni 0.6 O 4 and SiO 2 /Co 2.4 Ni 0.6 O 4 Oxides for Thermochemical Energy Storage.

Author

Portilla-Nieto, Yasmina, Bielsa, Daniel, Dauvergne, Jean-Luc, Hernaiz, Marta, Aranzabe, Estibaliz, Doppiu, Stefania, and Palomo del Barrio, Elena

Subjects
ENERGY storage, HEAT storage, ACTIVATION energy, DISCONTINUOUS precipitation, METALLIC oxides
Abstract

One of the possible solutions for the transition of the actual energetic model is the use of thermal energy storage technologies. Among them, thermochemical energy storage based on redox reactions involving metal oxides is very promising due to its high energy density. This paper deals with the development of the kinetic study based on data extracted from the thermogravimetric analysis of a cobalt-nickel mixed oxide (Co2.4Ni0.6O4) without and with the addition of SiO2 particles to improve the cyclability. The results show that in the reduction reaction the activation energy is not affected by the addition of SiO2 particles while in the oxidation reaction an increase in the activation energy is observed. The theoretical models fitting with the experimental data are different for each material in the reduction reaction. The mixed oxide is controlled by a nucleation and growth mechanism for conversion ratios higher than 0.5, while the added material is controlled by diffusion mechanisms. In the oxidation reaction, the two materials are controlled by a nucleation and growth mechanism for conversion ratios higher than 0.5. [ABSTRACT FROM AUTHOR]

Published
2022
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32. Non-Immersion Ultrasonic Cleaning for Heliostats.

Author

Ander Sarasua, Jon, Sandá, Alejandro, Villasante, Cristobal, and Aranzabe, Estibaliz

Subjects
ULTRASONIC cleaning, HELIOSTATS, DUST, WATER jets, ULTRASONIC equipment
Abstract

Soiling and dust accumulation in reflectors for concentrating solar plants (CSP) decrease their reflectance and, as a consequence, the solar field efficiency [1]. Most widely used cleaning methods are based on pressured water jets and rotary brush cleaners. Each method has its own advantages and drawbacks. On one hand, pressured water jets can reach up to 97% of relative reflectance [1] without any kind of physical contact, but it supposes a great amount of demineralized water consumption. On the other hand, brush cleaners consume less water and give higher cleaning efficiency (almost 100% of relative reflectance) but because of the physical contact between the brush and the surface of the mirror, which is full of hard dust particles, mirror's surface is exposed to abrasion that reduces its reflectivity permanently. The present paper describes the work done on the development of a novel cleaning method based on the same principles of the well known ultrasonic cleaning. This method has demonstrated to be the most efficient one in the market but it is limited to objects that can be immersed. The cleaning of a heliostat would not be feasible with this technology. Most part of the work of the present research has been focused is the development of an ultrasonic device that needs no immersion and, of course, no contact. The system has been tested on real mirror probes at different process conditions and it has been compared with conventional pressured water jet cleaning. It has demonstrated be able to obtain better cleaning results (up to 99% of relative reflectance) with about 600 times less water. [ABSTRACT FROM AUTHOR]

Published
2018
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34. Invigorating polyurethane foams with phase change materials supported in inorganic containers.

Author

Goitandia, Amaia M., Beobide, Garikoitz, Vadillo, Julen, Del Val, Ignacio, Aranzabe, Estibaliz, and Aranzabe, Ana

Subjects
URETHANE foam, PHASE change materials, MICROENCAPSULATION, THERMAL insulation, COMPRESSIVE strength
Abstract

The present study covers the development and testing of polyurethane (PU) foams modified with phase change materials (PCMs) supported in inorganic silica containers. Two kind of inorganic supports (mesoporous silica and tight silica microcapsules) were selected as representative cases of two alternatives for the preparation of phase change composites: infiltration of PCMs on porous supports and microencapsulation of PCMs. The two types of phase change composites exhibit latent heats of 100–130 J·g−1 and PCM uptakes of 45–60%. The addition of the phase change composites to the formulation of a rigid PU foam promoted subtle changes in the foam growth process which were responsible of a cell‐size contraction and of strengthening the compressive strength in a 27–30%. The thermal performance of the PU foams was tested under isothermal laboratory conditions showing higher thermal storage capacity in doped foams. Additionally, the higher energy storage capacity of the modified foams provides them greater thermal inertia. POLYM. COMPOS., 39:1420–1432, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Published
2018
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38. Metal-organic aerogels based on titanium(IV) for visible-light conducted CO2photoreduction to alcohols

Author

Angulo-Ibáñez, Adrián, Perfecto-Irigaray, Maite, Merino-Garcia, Ivan, Luengo, Naia, Goitandia, Amaia M., Albo, Jonathan, Aranzabe, Estibaliz, Beobide, Garikoitz, Castillo, Oscar, and Pérez-Yáñez, Sonia

Abstract

Metal-organic frameworks (MOFs) imply an appealing source of photocatalysts as they combine porosity with tailorable electronic properties and surface chemistry. Herein, we report a series of unprecedented metal-organic aerogels (MOAs) comprised by Ti(IV) oxo-clusters and aromatic dicarboxylic linkers as an alternative to microporous MIL-125 and MIL-125-NH2MOFs. Discrete titanium oxo-clusters polymerized upon the addition of the dicarboxylic linkers to give rise to a metal-organic gel. Their supercritical drying led to aerogels comprised by nanoscopic particles (ca. 5–10 nm) cross-linked into a meso/macroporous microstructure with surface area ranging from 453 to 617 m2·g−1, which are comparatively lower than the surface area of the microporous counterparts (1336 and 1145 m2·g−1, respectively). However, the meso/macroporous microstructure of MOAs can provide a more fluent diffusion of reagents and products than the intrinsic porosity of MOFs, whose narrower channels are expected to imply a more sluggish mass transport. In fact, the assessment of the continuous visible-light-driven photocatalytic CO2reduction into methanol shows that MOAs (221–786 μmol·g−1·h−1) far exceed not only the performance of their microporous counterparts (49–65 μmol·g−1·h−1) but also surpass the production rates provided by up-to-date reported photocatalysts.

Published
2022
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39. Development and stabilization of Co2.4Ni0.6O4material for long-term thermochemical energy storage

Author

Portilla-Nieto, Yasmina, Vidal, Karmele, Hernaiz, Marta, Aranzabe, Estibaliz, Doppiu, Stefania, and Palomo del Barrio, Elena

Abstract

Redox thermochemical energy storage is one of the most promising technologies to achieve dispatchability in concentrated solar power applications. Compared to commercially available thermal energy storage technologies, Redox thermochemical storage provides much higher energy storage capacity and allows energy storage at temperatures beyond 600 °C. In addition, metal oxides supporting redox reactions are usually non-critical, low-cost materials.

Published
2022
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40. Tribological behaviour of the low and high viscosity peek at various testing scales

Author

Rodriguez Fereira, Vanessa, Sukumaran, Jacob, Perez Delgado, Yeczain, De Baets, Patrick, Igartua, Amaia, Fernandez, Beatriz, Schlarb, Alois K, Aranzabe, Ana, Igartua, Amaya, Arnaiz, Aitor, Aranzabe, Estibaliz, and Barriga, Javier

Subjects
Technology and Engineering, friction and wear, polyetheretherketone PEEK, sliding bearing, injection viscosity
Abstract

Polyetheretherketone (PEEK) has become most attractive as a sliding bearing material in industrial applications, due to its excellent thermal stability, good friction and wear resistance. These properties promote the material to be used in so called high performance tribological applications. However, fundamental mechanisms governing friction and wear are not yet fully understood and neither is the influence of composition parameters. An important parameter is PEEK’s viscosity during injection moulding which is heated up to semi-solid state, between its glass transition and melting temperature. It is not known to what extent the injection viscosity, related to the applied temperature profile, affects subsequent tribological features. This paper studies the friction and wear performance of low and high viscosity PEEK under dry reciprocating sliding contact. The tests were performed with small and large scale specimens under pin-on-plate and flat-on-flat configuration, respectively; to determine the transitions in tribological behaviour at different scales and to identify the applications limits. Tests were carried out at controlled atmosphere with 25 °C and a relative humidity of 50%. Parameters such as contact pressures and sliding speed were limited at 10 MPa and 20 mm/s, respectively; post mortem analyses were carried out by means of 2-D surface topography and optical microscopy. The results show that PEEK injected at high viscosity exhibits a tribological performance with a relatively high coefficient of friction and high wear rate compare to PEEK injected at low viscosity.

Published
2012

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